AbstractMany recent publications related to audio coding use the recommendation "MUltiple Stimuli with Hidden Reference and Anchor" (MUSHRA; ITU-R BS.1534-1) for the evaluation of subjective audio quality. Judging the quality of multiple conditions can be inconclusive if the employed test excerpts exhibit more than one prevalent artifact. Two papers investigate the impact of time varying artifacts in both, synthetic and real world signals and claim "perceptual stationarity" as a requirement for test sequences used in MUSHRA tests. This first part deals with commonly used test signals. These often have a length of 10 to 20 seconds and frequently contain time varying perceptual artifacts. Ratings of those items are compared to ratings of cutouts that are predominantly perceptually stationary over time.